More than 80% of the industrially produced chemicals are prepared by catalytic processes. Catalytic processes are generally more economically viable and environmentally friendly than corresponding stoichiometric organic reactions. The homogeneous catalysts used, in addition to acids and bases, are in particular complexes of the noble metals. Nickel, palladium and platinum complexes also find use as homogeneous catalysts in numerous industrial processes and in organic synthesis on the laboratory scale. An important example is the utilization of aryl-X compounds (X=halogen, OTf, N2+, OMs, C(O)Cl etc.). Especially bromo- and chloroaromatics are versatile intermediates of the chemical industry, for example as precursors for the preparation of agrochemical intermediates, pharmaceuticals, dyes, materials, etc. In addition, nickel and palladium catalysts are frequently employed catalysts for the functionalization of haloaromatics or vinyl halides to aromatic olefins and dienes respectively (Heck reaction, Stille reaction), biaryls (Suzuki reaction, Stille reaction, Kumada reaction, Negishi reaction), alkynes (Sonogashira reaction), carboxylic acid derivatives (Heck carbonylation), amines (Buchwald-Hartwig reaction.
The catalyst systems described for olefinations, alkynylations, carbonylations, arylations, aminations and similar reactions of aryl-X compounds frequently have satisfactory catalytic turnover numbers (TON) only with uneconomic starting materials such as iodoaromatics and activated bromoaromatics. In contrast, in the case of deactivated bromoaromatics and especially in the case of chloroaromatics, generally large amounts of catalyst have to be added in order to attain industrially useful yields (>90%). Owing to the complexity of the reaction mixtures, simple catalyst recycling is additionally not possible, so that even the recycling of the catalyst causes high costs which are generally an obstacle to industrial implementation. In addition, particularly in the case of the preparation of active ingredients or active ingredient precursors, it is undesired to work with large amounts of catalyst, since there is the risk in this case that catalyst residues remain in the product. Relatively recent catalyst systems are based on cyclopalladated phosphines (W. A. Herrmann, C. Broβmer, K. Öfele, C.-P. Reisinger, T. Priermeier, M. Beller, H. Fischer, Angew. Chem. 1995, 107, 1989; Angew. Chem. Int. Ed. Engl. 1995, 34, 1844) or mixtures of sterically demanding arylphosphines (J. P. Wolfe, S. L. Buchwald, Angew. Chem. 1999, 111, 2570; Angew. Chem. Int. Ed. Engl. 1999, 38, 2413) or tri-tert-butylphosphine (A. F. Littke, G. C. Fu, Angew. Chem. 1998, 110 3586; Angew. Chem. Int. Ed. Engl. 1998, 37, 3387) with palladium salts or palladium complexes.
However, inexpensive chloroaromatics cannot always be derivatized in an industrially satisfactory manner by means of the above-described reactions even using such catalysts. The catalyst productivities (expressed as TON) for the reactions mentioned are typically below 10,000, and the turnover frequencies (TOF) below 1,000 h−1. Thus, for the achievement of high yields, comparatively high amounts of the expensive catalysts have to be used. In spite of all further developments of the catalysts in recent years, only few industrial implementations of the arylation, carbonylation, olefination, etc., of chloroaromatics have become known to date.
An important example of the industrial use of platinum catalysts is hydrosilylation, for example in the preparation of organosilanes or in the crosslinking of silicone rubber. In such reactions too, the productivity and the reactivity of the catalyst is of course a considerable factor for its industrial employability.
The active palladium catalysts which are commonly used in the context of the activation and further utilization of aryl-X compounds are palladium(0) complexes. The situation is similar for nickel catalysts. Platinum catalysts which are used for the hydrosilylation are platinum(IV), platinum(II) and platinum(0) complexes, of which especially the platinum(0) complexes have high activity and have found widespread use.